Silica crucible with inner layer crystallizer and method

ABSTRACT

A silica glass crucible is disclosed comprising a barium-doped inner wall layer. The crucible is made by introducing into a rotating crucible mold bulk silica grain to form a bulky wall. After heating the interior of the mold to fuse the bulk silica grains, an inner silica grain, doped with barium, is introduced. The heat at least partially melts the inner silica grain, allowing it to fuse to the wall to form an inner layer. The inner layer of the crucible crystallizes when used in a CZ process, extending the operating life of the crucible.

BACKGROUND OF THE INVENTION

[0001] The present invention is related to the field of silicacrucibles, and more specifically to a silica crucible having amulti-layer wall in which one or more of the wall layers are doped withbarium.

[0002] The Czochralski (CZ) process is well-known in the art forproduction of ingots of single crystalline silicon, from which siliconwafers are made for use in the semiconductor industry.

[0003] In a CZ process, metallic silicon is charged in a silica glasscrucible housed within a susceptor. The charge is then heated by aheater surrounding the susceptor to melt the charged silicon. A singlesilicon crystal is pulled from the silicon melt at or near the meltingtemperature of silicon.

[0004] A current trend in the semiconductor industry is toward largediameter wafers, e.g., 300-400 mm in diameter. As a result, the CZprocess operating period must be concomitantly increased, sometimes tomore than one hundred hours. Also, structural defects in the siliconcrystal can be reduced by slowing down the pulling rate, which in turnprolongs the CZ run time and emphasizes the need to improve the usefullife of the crucible.

[0005] At operating temperatures, the inner surface of a silica cruciblefrequently reacts with the silicon melt. In many cases, the innersurface of the crucible undergoes a change in morphology. The innersurface of a crucible is seen to roughen during prolonged operation in aCZ run. This roughening, and the phase transformation underlying it, areaddressed in greater detail below.

[0006] This roughening can cause a loss of crystal structure of thepulled ingot. Inner surface roughening renders the crucible unfit foruse in silicon ingot manufacture. When a major portion of the innersurface of the crucible is covered by a rough surface, crystallinestructure is disrupted at the crystal-melt interface. Such a roughenedcrucible is unsuitable for ingot manufacture and silicon crystal pullingusing a roughened crucible must be ceased to avoid manufacture ofsubstandard ingots.

[0007] Additionally, the inner surface of a silica glass crucible canpartially dissolve into the silicon melt during the CZ process. Siliconand oxygen, the main components of a silica crucible, are notdeleterious to the silicon melt. However, impurities in the inner layerof the crucible can be transferred to the silicon melt during thisprocess. The quality of the pulled single crystal may be ruined,depending on the extent of contamination and the nature of thecontaminant.

[0008] One such effort to control inner surface morphology is a cruciblewith barium-containing chemicals coated onto the inner surface. U.S.Pat. Nos. 5,976,247 and 5,980,629, both to Hansen et al., disclose acrucible incorporating a devitrification promoter on the inner surfaceof the crucible. The devitrification promoter is taught to preventparticulate generation at the silica-melt interface. The devitrifiedlayer, created during a CZ run, is described in these references as acrystallized silica layer and is reported to dissolve uniformly andmaintain a smooth crucible inner surface.

[0009] Barium carbonate (BaCO₃) is disclosed as a preferred coatingmaterial, although other alkaline-earth metal compounds are disclosed.Coating is done as a post-treatment of a finished crucible by applying asolution of barium-containing chemicals. The coated crucible is thendried using clean, hot air.

[0010] If the crystalline layer thickness exceeds a certain level, thecrucible is prone to cracks and possible leakage of the silicon melt.Despite careful optimization of the barium coating level, the cruciblenevertheless occasionally experiences cracking toward the end of a CZrun.

[0011] However, devitrification (i.e., crystallization) occurs in ashallow layer on the inner surface of the crucible. The silica glass socoated experiences a large volume change as it crystallizes when bariumcoating is used as a crystallization promoter. The volume change createsstress at the glassy phase-crystalline phase interfaces. Such stress isrelieved by micro-scale deformation in the glassy phase of the crucible.

[0012] Other drawbacks to barium coating include difficulty incontrolling the thickness and uniformity of barium per unit area on thecrucible surface. The drying procedure is also prone to introduceairborne contamination.

[0013] Additionally, BaCO₃ is poorly soluble in water, but the coatingcan be easily removed by rinsing or wiping the inner surface with water.Normal cleaning procedures (e.g., rinsing, etching or wiping) cannot beperformed after barium coating. Crucibles must also be carefully storeduntil used.

[0014] One of the present inventors filed Japanese Patent 3100836 (laidopen Tokukai Hei8-2932), which teaches an inner layer of 0.5-1 mm inthickness and containing from 0.1-2% aluminum by weight. The inner layercrystallizes during the CZ process, such that inner surface dissolutionis suppressed and the dimensional stability of the crucible is improved.

[0015] However, aluminum may dissolve into the silicon melt andsubsequently lodge in the silicon crystal. The level of aluminumcontamination of the crystal can be successfully controlled in somecases. Nevertheless, there are applications wherein aluminumcontamination is undesirable.

SUMMARY

[0016] The present disclosure provides a silica glass cruciblecomprising a wall with a barium-doped layer formed as an integral partof the crucible. The inner layer is doped with barium at a concentrationsuch that the inner layer will rapidly crystallize upon heating.Utilization of a doped layer, rather than a coating on the interiorsurface, permits the crucible to be handled and processed without damageto the barium-doped inner layer.

[0017] A method is disclosed for making a silica crucible having aninner layer doped so as to devitrify during a CZ run. The methodcomprises introducing into a rotating crucible mold bulk silica grain,consisting essentially of quartz grain, to form a bulky wall. Afterheating the interior of the mold to fuse the bulk silica grains, aninner silica grain, doped with barium, is introduced into the mold. Theheat also at least partially melts the inner silica grain, allowing itto fuse to the wall to form an inner layer. The crucible thus formed iscooled then taken out of the mold.

[0018] The invention will become more readily apparent from thefollowing detailed description, which proceeds with reference to thedrawings, in which:

BRIEF DESCRIPTION OF DRAWINGS

[0019]FIG. 1 is a cross-sectional view of one embodiment of a silicaglass crucible constructed according to the present disclosure.

[0020]FIG. 2 is an enlarged, partial cross-sectional view of the wall ofthe silica glass crucible shown in FIG. 1.

[0021]FIG. 3 is an enlarged, partial cross-sectional view of the wall ofa second embodiment of a silica glass crucible constructed according tothe present disclosure.

[0022]FIG. 4 is an enlarged, partial cross-sectional view of the wall ofa third embodiment of a silica glass crucible constructed according tothe present disclosure.

[0023] FIGS. 5-6 are diagrams showing a method for making the silicaglass crucible shown in FIGS. 1-2.

[0024] FIGS. 7-8 are diagrams showing a method for making the secondembodiment silica glass crucible shown in FIG. 3.

[0025]FIG. 9 is a diagram showing the initial step of forming an outerlayer, to form the third embodiment silica glass crucible of FIG. 4.

[0026] FIGS. 10A-10C are plan views of a prior art crucible innersurface at various stages of a CZ run.

[0027]FIG. 11 is an enlarged cross-sectional view of the portion of acrucible constructed according to the present disclosure, in which theinner layer is crystallized.

DETAILED DESCRIPTION OF EMBODIMENT(S)

[0028] In more detail, the present disclosure provides a silica glasscrucible suitable for use in a CZ process. One embodiment of thecrucible is shown in FIGS. 1-2. A silica glass crucible 1 has a wall 10defining an interior cavity 12. The wall 10 comprises a side portion 10a and bottom portion.

[0029] The side portion 10 a of this embodiment comprises a bulk layer14 of pure silica and an inner layer 16 formed on the inner portion ofthe wall. The bulk layer 14 generally is a translucent glass layerconsisting essentially of silica. The inner layer 16 is comprised offused doped silica.

[0030] The inner layer 16 in the embodiment of FIGS. 1-2 is doped withbarium in the range of 5-150 ppm, and preferably 15-75 ppm. In theillustrated embodiment, the inner layer has a thickness in the range of0.2 mm-1.0 mm.

[0031] In other embodiments, a thin barium-doped layer can be formed ona transition layer of synthetic silica glass or pure silica glass, thelatter made from purified natural quartz. Such an embodiment is shown inan enlarged cross-sectional view in FIG. 3. The side portion 10 a ofthis embodiment comprises a bulk layer 14, an inner layer 16, and atransition layer 18. As in the embodiment of FIGS. 1-2, the bulk layer14 is typically translucent silica glass, and the inner layer 16likewise is doped with barium element as described below.

[0032] The transition layer 18 can be non-doped silica glass, made fromnatural or synthetic silica grain. Alternatively, however, variousmaterials can be employed in the transition layer. For example, thetransition layer can be a doped layer. The dopant can be an element thesame or different than that used in the inner layer.

[0033] In the alternative embodiment of the crucible shown in FIG. 4, adoped layer is also formed on the outer portion of the wall 19. In oneembodiment, the outer layer 19 is approximately 0.5-2.5 mm in thicknessand can be doped with aluminum in the range of about 50-500 ppm. Inanother embodiment, the outer layer is doped with aluminum in the rangeof about 100-500 ppm.

[0034] In a representative crucible, the side portion 10 a has athickness of approximately 10.0 mm, of which the inner layer 16comprises 0.2-1.0 mm, the outer layer 19 comprises 0.5-2.5 mm, and thebulk layer 14 comprises the remaining 6.5-9.4 mm.

[0035] The bottom portion can be constructed so as to have a similarstructure to the side portion 10 a of FIGS. 2-4, but is preferablyformed without a doped outer layer.

[0036] It should be apparent that a crucible can be constructed havingan inner layer 16, a transition layer 18, a bulk layer 14, and an outerlayer 19.

[0037] A method is disclosed herein for making a doped inner layeradapted to devitrify during a CZ run. The method shown in FIGS. 5-6 isfor making the crucible embodiment shown in FIGS. 1-2.

[0038] To form the bulk grain layer 36, the bulk grain hopper 22 a, flowregulating valve 26 a and feed tube 24 are used. In FIG. 5, bulk silicagrain 30 is introduced into a mold 20 to form the bulk grain layer 36.The bulk silica grain 30 is preferably pure quartz grain. Hopperstirring blade 28 a aids the uniform flow of grain from the hopper 22 a.

[0039] A scraper 32 shaped to conform to the inner surface of the mold,is generally used to shape the introduced bulk silica grain. In thismanner, the bulk grain layer 36 can be formed to a selected thickness.

[0040] Fusion of formed silica grain is shown in FIG. 6. An electrodeassembly, comprising a power source 37 and electrodes 38 a,38 b, ispositioned partially within the interior cavity of the rotating mold 20.An electric arc is produced between electrodes 38 a,38 b by supplying250-350V and approximately 1800A direct current. A region of heat 42 isthereby generated within the mold interior. This heat 42 serves to fuseformed bulk grain layer 36 in the mold.

[0041] Fusion proceeds through the formed grain from proximal to distal,relative to electrodes 38 a,38 b. The mechanism of progressive fusionthrough the silica grain layer according to this technique is known tothose skilled in the art, for example, as disclosed in U.S. Pat. Nos.4,935,046 and 4,956,208 both to Uchikawa et al.

[0042] Contemporaneous with fusion of the surface of the formed bulkgrain layer 36, inner silica grain 44 is poured from the inner silicagrain hopper 22 b through feed tube 40. Inner grain flow regulatingvalve 26 b can be utilized to control the rate at which inner layergrain 44 is introduced into the region of heat 42. Hopper stirring blade28 b also aids the homogeneity and uniform flow of grain from the hopper22 b.

[0043] The arc produced between the electrodes creates a very strongplasma field, propelling the partially melted inner silica grain 44outward, enabling it to be deposited on the sides and bottom of thecrucible inner surface. The inner grain 44 passes through the heatedregion 42, is at least partially melted by the arc flame therein, and isdeposited on the surface of the bulk layer, which is the fused bulkgrain layer 36.

[0044] The introduced inner grain 44 is fused to the bulk layer to forman inner layer 16. Molten inner grain thereby is continuously depositedand fused over a period of time of inner layer formation. The innerlayer 16 thus formed is essentially transparent and bubble-free. Thethickness of fused inner layer is controlled by the introduction rate ofinner silica grain and by the period of inner grain supply duringfusion.

[0045] Inner silica grain 44 consists essentially of pure silica grain,such as natural silica grain washed to remove contaminants, doped withbarium. Alternatively, synthetic silica grain doped with barium can beused.

[0046] In FIG. 6, the bulk layer is numbered as 36 representing bulkgrain layer for convenience. At this stage in the method, of course,this layer is actually a dynamic combination of fused bulk layer 14 andunfused bulk grain layer 36.

[0047] A method for making a crucible having both an inner layer and atransition layer comprises the steps shown in FIGS. 5 and 7-8.

[0048] After formation of a bulk grain layer 36, the electrode assemblyis positioned within the crucible interior cavity and a transition layer18 is fused to the partially fused bulk layer 14, in a manner similar todeposition of the inner layer as in FIG. 6.

[0049] Transition grain 48 is supplied from the transition grain hopper22 c through flow controlling valve 26 c. Hopper stirring blade 28 c canbe employed similarly to stirring blade 28 a.

[0050] After deposition of the transition layer 18, the hopper assemblyceases introduction of transition silica grain 48 by closing transitiongrain flow regulating valve 26 c. Inner grain 44, contained in hopper 22b, is then introduced via opening of flow regulating valve 26 b. Innergrain 44 is introduced into the region of heat 42, is at least partiallymelted and deposited as inner layer 16 on transition layer 18.

[0051] The thicknesses of transition layer 18 and inner layer 16 arecontrolled with the help of flow controlling valves 26 c,26 b,respectively. In the method shown in FIG. 7, the transition layer 18 isa transparent layer prepared between the inner layer 16 (typically alsotransparent) and the translucent bulk layer 14.

[0052] The barium-doped grain can be put on any kind of transparenttransition layer. For example, the transition layer 18 can be a puresilica layer, an aluminum-doped layer, or a layer doped with anotherdopant. In one embodiment, the barium-doped inner layer is deposited ona transparent layer of synthetic silica glass or pure silica glass madefrom purified natural quartz.

[0053] A similar method is used to construct the crucible shown in FIG.4. An outer grain layer is first formed in a rotating mold 20, as shownin FIG. 9 the thickness of the outer grain layer is controlled using ascraper 47.

[0054] An outer grain hopper 22 d communicates via a feed tube 24 withthe interior of the mold 20. The feed tube 24 can employ a valve 26 d toregulate the flow of outer silica grain 46 from the hopper 22 d to theinterior of the mold. Outer silica grain is flowed thereby into therotating mold. Rotation of the crucible mold provides sufficientcentrifugal force to retain the poured outer silica grain on the innerside surface of the mold as outer grain layer 49

[0055] If outer layer is prepared, it is preferable that it be dopedwith aluminum rather than barium. One reason is that disposal of unfuseddoped outer silica grain is more convenient if the dopant is aluminum,for environmental concerns.

[0056] Fusion is carried out so that unfused grain is preserved betweenthe mold 20 and fused bulk layer 14 (or outer layer 19, if present).Unfused bulk silica grain 30 (and unfused outer grain, if present) isleft on the exterior of the crucible. Thus, a rough, bubble-containingoutermost surface results. Unfused grain is disposed of in subsequentprocessing of the crucible, typically by sand-blasting and rinsing withwater.

[0057] Barium is chosen as the doping element, because a small amount ofbarium can crystallize the silica glass and if it is dissolved in thesilicon melt it will not be transferred to the silicon crystal in largeamount.

[0058] In the embodiment of the present method thus described, the innersilica grain 44 contains barium via doping. Barium can alternatively beintroduced contemporaneously with essentially pure silica grain, i.e., abarium-containing compound can be mixed with essentially pure innersilica grain. For example, barium carbonate (BaCO₃) can be placed in theinner grain hopper 22 b. A mixing blade 28 b can be used to ensureuniform distribution of the barium-containing compound in the innersilica grain. The inner silica grain and barium carbonate mixture thencan be flowed into the region of heat as described above. Theessentially pure silica grain can be either undoped natural or syntheticsilica grain.

[0059] In an alternative embodiment of the method, the barium-containingcompound can be separately introduced into the heated regioncontemporaneous with inner silica grain introduction. A separate bariumcompound hopper can be provided, containing, for example, BaCO₃. Thevalves controlling the inner grain hopper and the barium compound hoppercan both be opened, so as to flow concurrently.

[0060] Using this alternative method, in which the barium compound isintroduced concurrently with but separate from the inner silica grain,the transition silica grain can also be employed as the inner silicagrain. For example, the transition silica grain can be flowed to form atransition layer as described above. The transition hopper flow isstopped, and then both transition silica grain and barium compound areflowed simultaneously into the heated region.

[0061] In a similar embodiment, the transition layer can be formed asoriginally described, and then the barium compound flow can be initiatedcontemporaneous with the still-flowing transition silica grain, to formthereby the inner layer having a barium component therein. The bariumcompound flow rate can be variable, such that a barium gradient from theinner surface to the transition layer is formed.

[0062] In yet another example, the barium-containing compound can be inliquid form, e.g., an aqueous solution of barium hydroxide (Ba(OH)₂) orbarium chloride (BaCl₂). The liquid solution can be introduced into theinner silica grain 44 prior to or contemporaneous with introduction ofthe inner silica grain into the heated region, or the liquid solutioncan be introduced directly into the heated region. The latterintroduction can be accomplished by an injecting or misting device. Theinjecting device generally should be positioned adjacent the end of theflow tube proximate the heated region.

[0063] The inner layer in the crucible wall is doped with barium in therange of about 5-150 ppm, and most preferably between 15-75 ppm. Theinner layer preferably is free of bubbles, as bubbles entrapped withinthe inner layer may generate fracture-inducing particles as the layercrystallizes. Such particles can dissociate or break away from the innersurface as the bubble expands and as the inner surface erodes ordissolves into the silicon melt. Loose particles can cause loss of thesingle-crystal structure in the silicon ingot.

[0064] The method disclosed above dopes a crucible inner layer withbarium, rather than coating the interior surface of the crucible with abarium compound. This improved method, i.e., barium doping, has severalmerits over conventional coating methods.

[0065] The present method enables the concentration of barium in theinner layer to be finely controlled. In one embodiment of the presentmethod described above, the inner layer silica grain is doped withbarium prior to its introduction into the mold and fusion. The amount ofbarium contained in the barium-doped grain can be determined in advanceby analysis. The dopant level in the inner layer can thereby befine-tuned, for example, by mixing doped silica grain and pure silicagrain in the hopper.

[0066] The doped inner layer thickness can also be precisely controlledby changing inner silica grain flow rate or flow time. No loss of thebarium element was observed, e.g., loss due to sublimation.Substantially all of the introduced dopant was found to be fixed withinthe inner layer.

[0067] By doping with barium in the specified range as a crystallizationpromoter, the thickness of the crystallization in the layer iscontrolled. Only the region doped with barium crystallizes; regions notdoped with barium do not crystallize during a typical CZ-processoperation. This characteristic gives a crucible designer greater freedomto tailor the crucible to the needs of the process in which it will beemployed.

[0068] As the barium is fused in the silica glass, the crucibles can bemachined to dimensions, cleaned or etched, and handled with the sameprocedures as for normal pure silica crucibles; no additionalpost-manufacture processing or special handling of the crucible isrequired.

[0069] For example, unfused grain remaining on the outside of aconventional crucible is cleaned by sand-blasting, followed by rinsingwith water. After cutting the crucible to specified dimensions, it iscleaned by etching with dilute hydrofluoric acid and rinsing with purewater. The crucible is dried in a clean air bath, then bagged and boxedfor shipment. A user typically unpacks the crucible and again cleans itbefore use (by rinsing with water or wiping with alcohol or any othermethods as commonly used for pure silica glass crucibles). A crucibleconstructed according to the present disclosure can be handled asdescribed above.

[0070] It is known in the ingot manufacturing industry that circularpatterns (“rosettes”) are observed on the crucible surface contactingthe silicon melt. This phenomenon was determined to be a rosette 52surrounded by crystobalite (FIG. 10A). The center of the rosette has arough surface that may be covered by a very thin crystobalite layer.Outside of the rosette is the original silica glass surface 50, whichhas retained its original smoothness.

[0071] As CZ run time progresses, rosettes 52 grow and the surfaces ofthe rosette centers 54 become rough (FIG. 10B). Further, the rosettes 52merge and the rough surface area 54 increases, with a concomitantdecrease in the smooth virgin surface 50 (FIG. 10C).

[0072] The present crucible suppresses the generation of rosettes, whichstructures are the initial cause of the roughening of the inner surface.Rosette suppression is accomplished by crystallization of the innersurface of a crucible wall prior to full melt-down of the silicon chargein a CZ process.

[0073] Regarding these rosettes and concomitant surface roughening, thepresent disclosure employs barium doping to provide a mode forlengthening the useful life of a crucible suitable for use in aCZ-process. Generation of rosettes can be suppressed by crystallizingthe inner layer 16 of a crucible wall 14 (FIG. 11) prior to siliconcharge melt-down in a CZ-process. The inner layer undergoes a phasetransformation from fused silica glass to crystobalite 56, so that theinner surface 62 retains its smooth surface finish throughout.

[0074] In this mode, the inner surface 62 of the crucible is coveredwith crystobalite 56 before melt-down of the charged silicon. Rosettesare not formed by a reaction between the silicon melt and crystallinesilica. Because a rosette is not generated, a rough surface area doesnot appear and the inner surface remains smooth.

[0075] Some silicon ingot manufacturers perform sequential siliconcrystal “pulls” using the same crucible. In these uses, a subset of thecrucible side portion is alternately covered by the melt, exposed toatmosphere as the melt level drops, then covered again as silicon chargeis added to begin another ingot pull. The inner surface of a cruciblethus used is subjected to high stress for a longer time period, makingmore important the inner surface textural integrity.

[0076] The barium doping level in the inner layer and the thickness ofthe inner layer has an effect on the rapidity of crystallization in thelayer. Therefore, the depth and amount of barium doping in the innerlayer is important to achieve a fully crystallized inner layer.

EXAMPLES

[0077] Five crucibles A, B, C, D and E were manufactured according tothe present disclosure. As well, crucible P was constructed according tothe prior art. These crucibles have similar dimensions, e.g., nominaldiameters of 24 inches.

[0078] Barium doping levels were varied from 10-50 ppm for cruciblesA-E, and inner layer thickness was also varied from 0.2-0.8 mm.

[0079] The inner layer 16 of Crucibles A-E were made using abarium-doped inner silica grain. Crucibles A-D were made according tothe above-disclosed method, with the inner layer thicknesses and dopinglevels as follows: crucible A, 0.8 mm layer at 10 ppm; crucible B, 0.5mm layer at 25 ppm; crucible C, 0.2 mm layer at 50 ppm, and crucible D,1.0 mm layer at 50 ppm. Crucible E is a comparative embodiment, madewith an inner layer of 0.1 mm layer at 50 ppm.

[0080] The prior art crucible P was of 24-inch diameter. A 1.0 mm-thickinner layer was formed in its interior using pure natural silica graininstead of barium-doped inner silica grain. This natural silica graincontained trace amounts (<0.1 ppm) of barium and roughly 8 ppm aluminum.

[0081] Crucibles A-E and P were used in a 120-hour CZ-process, i.e., 120hours at the chosen high temperature including melting of the siliconcharge. The results of these processes are described below.

[0082] Crucibles A-E and P were subjected to a 120-hour CZ-process,after which the inner layer was examined. The smooth inner surface ofcrucibles A-D were found to consist essentially of crystobalite, with norosette pattern evident. The crucible inner surface presented a smoothfinish.

[0083] The 200-mm diameter silicon crystals made using crucibles A-Dwere also assessed. Dislocations were not observed in the siliconingots.

[0084] Crucible E, in contrast, was observed to have spot-wisecrystallization of the inner layer, with surface roughening occurring inthe non-devitrified loci. The CZ run using crucible E was terminatedafter 95 hours, as the silicon crystal experienced loss of structure. Itis concluded that the thickness of a barium-doped inner layer should begreater than 0.1 mm for the present crucibles.

[0085] Prior art crucible P was started in a similar 120-hourCZ-process. However, at about 80 hours into the process, the nascentsilicon ingot incurred a grain boundary flaw that disrupted its crystalstructure. This flaw forced termination of the CZ-process and renderedthe silicon crystal unsuitable for use in semiconductor manufacture.

[0086] Examination of the inner surface of Crucible P revealed that itwas roughened and almost totally covered with merged rosettes, with verylittle of the virgin glassy surface remaining. The rough texture withinthe rosette rings likely was the cause of the silicon crystalinterference.

[0087] A person skilled in the art will be able to practice the presentinvention in view of the description present in this document, which isto be taken as a whole. Numerous details have been set forth in order toprovide a more thorough understanding of the invention. In otherinstances, well-known features have not been described in detail inorder not to obscure unnecessarily the invention.

[0088] While the invention has been disclosed in its preferred form, thespecific embodiments thereof as disclosed and illustrated herein are notto be considered in a limiting sense. Indeed, it should be readilyapparent to those skilled in the art in view of the present descriptionthat the invention can be modified in numerous ways. The inventorregards the subject matter of the invention to include all combinationsand sub-combinations of the various elements, features, functions and/orproperties disclosed herein.

1. A crucible comprising: a wall having a side portion and a bottomportion thereby defining an interior cavity, said wall comprising: abulk layer; and an inner layer doped with barium.
 2. The crucible ofclaim 1, wherein the inner layer is in the range of 0.2-1.2 mm deep. 3.The crucible of claim 1, wherein the inner layer is doped with barium inthe range of about 5-150 ppm.
 4. The crucible of claim 3, wherein theinner layer is doped with barium in the range of about 15-75 ppm.
 5. Thecrucible of claim 1, the wall further comprising a metal-doped outerlayer formed on an outer portion of said wall.
 6. The crucible of claim5, wherein the outer layer is substantially an outer layer of the sideportion.
 7. The crucible of claim 5, wherein the outer layer issubstantially 0.5-2.5 mm deep.
 8. The crucible of claim 5, wherein theouter layer is doped with aluminum in the range of about 100-500 ppm. 9.The crucible of claim 1, wherein said inner layer is at least partiallycrystallized.
 10. The crucible of claim 1, wherein said inner layer isadapted to substantially completely crystallize prior to full melt-downof a silicon charge in a Czochralski process.
 11. A method for making asilica glass crucible, comprising: forming a bulk grain layer on aninterior surface of a rotating crucible mold, said bulk grain layerhaving a bottom portion, a side portion and a bulk grain layer interiorsurface; generating a region of heat in the interior of the mold,wherein the region of heat at least partially fuses said bulk grainlayer to form a bulk layer; and depositing a barium-containing innerlayer on the bulk grain layer interior surface.
 12. The method of claim11, wherein forming a bulk grain layer comprises introducing into therotating crucible mold bulk silica grain.
 13. The method of claim 12,wherein bulk silica grain consists essentially of quartz grain.
 14. Themethod of claim 11, wherein a selected thickness of the inner layer isin the range of 0.2-1.0 mm.
 15. The method of claim 11, whereindepositing a barium-containing inner layer comprises introducing intosaid mold inner silica grain doped with barium, wherein the region ofheat at least partially melts said inner silica grain and fuses said atleast partially molten inner silica grain to the bulk layer.
 16. Themethod of claim 15, wherein the inner silica grain is doped with bariumin the range of 5-150 ppm.
 17. The method of claim 15, wherein the innersilica grain is doped with barium in the range of 15-75 ppm.
 18. Themethod of claim 11, wherein depositing a barium-containing inner layercomprises introducing into said mold inner silica grain and barium, andwherein the region of heat at least partially melts said inner silicagrain and fuses said at least partially molten inner silica grain to thebulk layer.
 19. The method of claim 18, wherein the inner silica grainconsists essentially of natural silica grain.
 20. The method of claim18, wherein the inner silica grain consists essentially of syntheticsilica grain.
 21. The method of claim 18, wherein the barium is a solidcompound admixed with the inner silica grain.
 22. The method of claim21, wherein the solid barium compound is admixed with the inner silicagrain prior to introducing into said mold inner silica grain and barium.23. The method of claim 11, further comprising, prior to forming a bulkgrain layer: forming an outer grain layer on an interior surface of arotating crucible mold, wherein the region of heat at least partiallyfuses said outer grain layer to form an outer layer.
 24. The method ofclaim 23, wherein the outer layer is formed substantially on the sideportion.
 25. The method of claim 23, wherein forming an outer grainlayer comprises introducing into the rotating crucible mold outer silicagrain.
 26. The method of claim 25, wherein the outer silica grain isdoped with aluminum in the range of 100-500 ppm.
 27. A cruciblecomprising: a wall having a side portion and a bottom portion therebydefining an interior cavity, said wall comprising: a bulk layer; aninner layer formed, said inner layer being doped with barium; and atransition layer formed between the inner layer and the bulk layer. 28The crucible of claim 27, wherein the inner layer is in the range of0.2-1.2 mm deep.
 29. The crucible of claim 27, wherein the inner layeris doped with barium in the range of about 5-150 ppm.
 30. The crucibleof claim 29, wherein the inner layer is doped with barium in the rangeof about 15-75 ppm.
 31. The crucible of claim 27, wherein the transitionlayer is free of barium doping.
 32. The crucible of claim 31, whereinthe transition layer consists essentially of pure natural silica glass.33. The crucible of claim 31, wherein the transition layer consistsessentially of pure synthetic silica glass.
 34. The crucible of claim27, wherein the transition layer is doped with a metal.
 35. The crucibleof claim 34, wherein the metal is aluminum.
 36. The crucible of claim27, further comprising an aluminum-doped outer layer formed on anexterior aspect of the wall.
 37. The crucible of claim 36, wherein thealuminum-doped outer layer is substantially an outer layer of the sideportion of the wall.
 38. The crucible of claim 36, wherein the outerlayer is no more than substantially 0.5-2.5 mm deep.
 39. The crucible ofclaim 36, wherein the outer layer is doped with aluminum in the range ofabout 100-500 ppm.
 40. The crucible of claim 27, wherein said innerlayer is at least partially crystallized.
 41. The crucible of claim 27,wherein said inner layer is adapted to substantially completelycrystallize prior to full melt-down of a silicon charge in a Czochralskiprocess.
 42. A method for making a silica glass crucible, comprising:forming a bulk grain layer on an interior surface of a rotating cruciblemold; generating a region of heat in the interior of the mold, whereinthe region of heat at least partially fuses said bulk grain layer toform a bulk layer; depositing a transition layer on the bulk grainlayer; and depositing a barium-containing inner layer on the transitionlayer.
 43. The method of claim 33, wherein a selected thickness of theinner layer is in the range of 0.2-1.0 mm.
 44. The method of claim 42,wherein forming a bulk grain layer comprises introducing into a rotatingcrucible mold bulk silica grain.
 45. The method of claim 44, wherein thebulk silica grain consists essentially of quartz grain.
 46. The methodof claim 42, wherein depositing a transition layer comprises introducinginto a rotating crucible mold transition silica grain, wherein theregion of heat at least partially melts said transition silica grain andfuses said at least partially molten transition silica grain to the bulklayer to form a transition layer.
 47. The method of claim 46, whereinthe transition silica grain consists essentially of pure natural silicagrain.
 48. The method of claim 46, wherein the transition silica grainconsists essentially of pure synthetic silica grain.
 49. The method ofclaim 46, wherein the transition silica grain is doped with a metal. 50.The method of claim 49, wherein the metal is aluminum.
 51. The method ofclaim 42, wherein a selected thickness of the inner layer is in therange of 0.2-1.0 mm.
 52. The method of claim 42, wherein depositing abarium-containing inner layer comprises introducing into said mold innersilica grain doped with barium, wherein the region of heat at leastpartially melts said inner silica grain and fuses said at leastpartially molten inner silica grain to the bulk layer.
 53. The method ofclaim 52, wherein the inner silica grain is doped with barium in therange of 5-150 ppm.
 54. The method of claim 52, wherein the inner silicagrain is doped with barium in the range of 15-75 ppm.
 55. The method ofclaim 42, wherein depositing a barium-containing inner layer comprisesintroducing into said mold inner silica grain and barium, and whereinthe region of heat at least partially melts said inner silica grain andfuses said at least partially molten inner silica grain to the bulklayer.
 56. The method of claim 55, wherein the inner silica grainconsists essentially of natural silica grain.
 57. The method of claim55, wherein the inner silica grain consists essentially of syntheticsilica grain.
 58. The method of claim 55, wherein the barium is a solidcompound admixed with the inner silica grain.
 59. The method of claim58, wherein the solid barium compound is admixed with the inner silicagrain prior to introducing into said mold inner silica grain and barium.60. The method of claim 42, further comprising, prior to forming a bulkgrain layer: forming an outer grain layer on an interior surface of arotating crucible mold, wherein the region of heat at least partiallyfuses said outer grain layer to form an outer layer.
 61. The method ofclaim 60, wherein the outer layer is formed substantially on the sideportion.
 62. The method of claim 60, wherein forming an outer grainlayer comprises introducing into the rotating crucible mold outer silicagrain.
 63. The method of claim 62, wherein the outer silica grain isdoped with aluminum in the range of 100-500 ppm.